Magnetron



Nov. 2.7, 1951 c. w. HANsELl.

MAGNETRON 2 SHEETS- SHEET 1 MAW/776' f nimm/A Filed Feb. 21, 1946 WFL /Af/A ATTO R N EY Nov. 27, 1951 c. w. HANSELL MAGNETRON l N V E N TO R Mii/Vai MHH/WELL ATTORN EY Patented Nov. 27, 1951 MAGNETRON Clarence W. Hansell, PortlJeHv-erson, N. Y...

assignor to Radio Corporation of America, a.

corporation of Delaware Application February 21, 1946, Serial No. 649,342

9 Claims.

This invention relates to an electron discharge device and circuits therefor, and particularly to magnetron amplifiers.

In the oscillating space charge inside a magnetron oscillator, the forces which determine the oscillation, or which are essential for oscillation, are relatively small at a location close to the cathode but relatively large at a loca-tion near the anode. In practicing the present invention, I contemplate making use of this phenomenon by introducing forces close to the cathode by means of power derived from an external source, in order to control ythe frequency or amplitude of oscillation, and thus obtain a large ratio of output power to input power.

The present invention overcomes a characteristie of the magnetron which is very undesirable from the standpoint of the user, and which is present in conventional magnetrons. In operating standard types of magnetron oscillators for continuous wave operation, it is necessary to raise the anode-to-cathode potential to some value near the cut-off potential (where all electron emission strikes the anode without returning to the cathode) in order to initiate oscillations. After oscillations have started, this potential must be reduced to a much lower value in order to obtain good eiiiciency of conversion of direct current power to alternating current power. By means of the present invention, I can control the magnetron to produce oscillations without the necessity for raising the anode-tocathode potential.

In accordance with the invention, I provide two or more control wires or rods near the cathode of the magnetron and apply alternating current potential between them in order to control the production of much larger alternating current potentials at the anode. This anode may take the form of two substantially semi-cylindrical segments or four arcuate-shaped segments symmetrically positioned around the cathode; or may take the form of a cavity resonator. The control wires or rods extend parallel to the cathode and are preferably positioned close to the cathode compared to the location of the anode. A magnetic field is utilized providing flux lines parallel to the axis of the cathode but transverse to the cathode-to-anode path.

A more detailed description of the invention follows in conjunction with a drawing, wherein:

Figs. 1 to 5 are cross-sections of five different v:magnetron embodiments of the present invention and circuits therefor, and

Fig. 4a is la section of the magnetron of Fig. 4 along the lines a-a, and also shows the oscillating eld and electron paths Within the magnetron.

Referring to Fig. l, there is Ishown a magnetron of the split anode type having an evacu- (ol. 315-39) v 2 -1 ated envelope E containing therein an indirectly heated linear cathode K and a pair of semicylindrical anode segments A, A, symmetrically positioned around the cathode. A coil or other suitable means for producing a magnetic field parallel to the cathode but transversely to the cathode-to-anode path is shown diagrammatically in dot and dash lines designated F. A pair of control wires or rods C, C are positioned physically parallel to each other and to the cathode but on opposite sides of and close to the cathode K. These control rods, wires or electrodes are used to start and control operation of the magnetron. Connected Ito these control rods C, C is a parallel tuned circuit M to which is magnetically coupled the alternating current from a source of radio frequency IN. This source may be a source of continuous waves of constant rfrequency and amplitude, or ya source of radio frequency signals. Connected to the anodes A, A is a parallel tuned output circuit N, and magnetically coupled to this output circuit N is a transmission line TL which passes the radio frequency energy abstracted from the magnetron to a suitable load shown as an antenna.

IIhe cathode K is supplied with heating current over a pair of leads extending to an iron core transformer T. The control rods C, C are maintained at a moderate positive potential relative to the cathode by means of a lead P, one end of which is connected to the electrical midpoint of the input ytuned circuit M and the other end of which is connected to a tap on a potentiometer R. Potentiometer R is connected between ground and a positive terminal of a source of unidirectional potential. It should be noted that this positive terminal is also connected to the electrical mid-point of the tuned output circuit N via lead S, thus supplying anode polarizing potential to the anode segments A, A. Radio frequency by-pass condensers D, D connect the leads P and S to ground, as shown.

In the operation of the system of Fig. 1, the two control rods or electrodes C, C are fed in opposite phase by the input alternating current from source IN. It should be noted, therefore, that the potential of one control rod C is varied relative to the other control rod C and that both of these control rods'vary in potential relative to the cathode and anode. Because the control rods are relativelyl close to the cathode, the radio frequency input power IN can be made to be relatively small compared to the output power which is derived from the output parallel tuned circuit N. These control rods C, C control'the output frequency or power of the magnetron by means of the relatively small electro-magnetic energy introduced close to the cathode. Output tuned circuit N may be resonant to the same frequency as input tuned circuit M or in har- 3 monic relation to the input frequency supplied to the control rods.

The system of the""invention is primarily adapted for use in magnetron amplifiers wherein continuous waves may be generated and synchronized by input power supplied to the control y rods C, C although it should be understood that, if desired, the input power Ymay be supplied in pulses, in which case the output power would also be in pulses of radio frequency energy.

In the operation of the invention, thecontrol rods C, C may be at a moderate positive potential relative to the cathode, or at a potential anywhere in a range from afmoderately negative potential Ito a moderately positive potential with respect-to the cathode, and in comparison Vwith the anode direct current potential, depending upon thedetaileddimensions of the magnetron lements, .particularly the cathode diameter. The anode direct current potential is usually comparativelyhigh in value comparedto the values ofthe other potentials applied to the electrodes ofthe magnetron.

Fig. `2 shows how the invention can be applied to fa magnetron having two pairs of arcuateshaped anode segments A', A and A", A", in whichoppositely located segments are directly connected-together andat 4the same radio frequency potential, while adjacent anode segments are "at instantaneously opposite radio frequency potentials. In Fig. 2 the control wires or rods C,'C are positioned-close to and physically parallel to the cathode but located between the cathode and anode segments having opposite instantaneous radio frequency potentials. Thus, one controlelectrode C is between the -cathode K and an ano-de Isegment A,`while the -other control electrode -C isconnected between the cathode K and another anode segmentA IThe 'two control rods or-wires C', C of Fig. 2 'are fedlby tuned input circuit M in opposite phase, inthe man-ner simi-lar tolthe way the control rods o-f-Fig. -1 are fed, although the control rods `of 2 are Ynot on opposite sides-of the cathode. lit-'should be noted that the control rods are adjacentianodesegments of V opposite .phase in .the

particular embodimentof Fig. 2. `The circuit elements `of AIig.` 2.1whic'h farethe same Aas those of the wave guide X can be dispensed with, and energy abstracted from the magnetron through a suitable probe yor coupling loop inserted into the cavity resonator. The probe or coupling loop can be connected to a suitable output transmission line extending to an antenna or other utilization circuit. The Cavity resonator W of Fig. 4 acts as the equivalent of a double anode in a double anode magnetron. The axial magnetic field has 'not been shown in Fig. 4 in the interest ofwsimplicity of the drawing. The electric iield of Fig. 4 is at rightangles to the cathode and at right angles to the drawing; that is, in a direction away from the eyes of the observer. The cavity resonator isresonant at rightangles t0 the illllS- tration ofFigA, oracross :the damelial dimension from left to right, or vice versa, of the showing of FigAa. Fig. 4a illustrates a section Aof Fig. 4 along the lines'a-a, andshows the oscillating :electric field Vand the electron paths. The plus .and minus signs on the control rods C, C designate the opposite instantaneous input poten- .tials on these ,electrodes applied by the alternatingcurrent input sourceIN. l

Fig -5 illustrates the invention applied to a multi-resonant cavity type .of magnetron having apluralityof inwardlyprojecting targets onv the anode .structure Z. This `cavity resonator structure Z acts as the anode and is sometimes called a scalloped type of anode. Input power is .supplied by .a source of radio frequency input current IN which is inductively coupled tov lead P extending rompotentiometer R lto the control rods C,

C. Lead P is tunedby means vof condenser D' each other.

. grounded, iasshow-n. A iield coilF provides an 1v have -been 'given the same reference vcharg. 'i

Fig. 3 is a modification-of Z'Fig. 2, wherein four controlrods lare utilized and symmetrically positioned around the ..cathode. Ilhesecontrol rods are `desig-nated C, lC :and -Cf C'f C" are connected together `and the rods C, Care connected together. One 4pair of rods C, C is connected to one side of the tuned .input .cir-cuit While -the other pair of rodsiC, C is connected to the other `terminal of the tuned input circuit M. All Vfour control rods fare positioned relatively close to and physically parallel to the cathode.

4Fig. 4 shows -thevinvention applied to a magnetron whoseanode is in the form of a cylindrical cavity resonator W. The .cathode rK `is .shown along the axis of =the .magetron, while .the two 'controllrods or .electrodes C, C are shown onopposite sides of thecathode K. .It should be noted thatoppositaend wallsof .the cavity resonator W have apertures which are sealedbyglass windows G. One-of the glass windowsG is utilized to :withdraw voutput Lenergyimm the magnetron, which ycan-*loe radiated :therethrough Vor fcarried away Yin aisuitablewaverguide X, .shown connected to the cavity resonator W. Obviously, if desired,

The rods C",

which is lslidable along. the lengths of lead P rand cathode lead P. This condenser is :a shorteircuit `ora' path of extremely low impedancefor energyof the inputfr-equency. f r

.It should .be noted that in this construction both .control rods C, lC are .directly connectedtogetherand .fed cophasally relative tothe cathode. The control rodSvC, -Care on Yopposite sides .of the cathode K and inelectrically parallel relation to Thescalloped anode structure 'Z is electromagnetic .iieild parallel to the cathodeand transversely to the anode-to-cathodepath. vOutput `from the magnetron -is ta-ken from a loop L which passes out through a -hole in the anode structure Z and connects to the inner conductor ofa coaxial line glass `'seal-J -seals ofl this hole 'inv-the cavity resonator. The frequency of the input source I-Nand the frequency of theoutput lenergy 'may be the sa-ine -or harmonica'lly -re lated to=ea-ch=other.

The general construction of the magnetron, exceptV for theuse'ofrthe--control 'rods (I2-C may be generally ofthe type describedi-n myf-Un-ited States-Patent 2,217,745,granted October 115, 1940.

Althoughthe present invention-has-b'een described as using -tw'oand Lfour control rods symmetrically 'positioned around Vthe cathode, it should be understood that l'sito or 'more -control rods -can also be employed ini-practicing 4the-invention along "the same principle loutlined above without departing -fro'mthe-spirit and scope of the "invention. y Y

K What is claimedlis:

-1. Afmagnetronfcornprising acathode, an anode structure having aplurality of yspaced -targetportions surrounding -said cathode, and a pairY of spaced control wires parallel `to and insulated from eachother and l-said cathode, ibutmspaced closerito fisai'd'- cathodeA than v-tosaid lanode structure, means for producing a magnetic eld acting transversely to the anode-to-cathode path, said control wires being arranged on opposite sides of said cathode, each of said control wires being arranged between said cathode and one of said target portions, and leads connected to said control wires for supplying alternating current input power thereto.

2. A magnetron amplifier comprising a cathode, an anode structure having a plurality of spaced target portions surrounding said cathode, a pair of spaced control wires parallel to and insulated from each other and said cathode but spaced closer to said cathode than to said anode structure, and each located on a straight line extending from said cathode to a point substantially centrally located relative to the ends of one of said target portions, means for producing a magnetic field acting transversely to the cathode-toanode path, a tuned circuit connected to said control wires to supply opposite instantaneous potentials thereto, a source of input radio frequency energy coupled to said tuned circuit, and means coupled to said anode structure for deriving from said anode structure radio frequency energy of larger power than said source of input power and of a frequency the same as or harmonically related to said input energy.

3. A magnetron comprising an evacuated envelope, a cathode within said envelope and along the axis thereof, an anode including a pair of arcuate shaped anode segments around said cathode, a pair of spaced control wires parallel to and insulated from each other and said cathode but spaced closer to said cathode than to said anode, one of said wires being positioned between said cathode and the central portion of one anode segment while the other wire is positioned between said cathode and the central portion of the other anode segment, a parallel tuned circuit connected to said control wires to supply opposite instantaneous potentials thereto, a source of radio frequency input power coupled to said tuned circuit, and means for producing a magnetic eld acting transversely to the cathode-to-anode path.

4. A magnetron comprising an evacuated envelope, a cathode within said envelope and along the axis thereof, an anode including a pair of arcuate shaped anode segments around said cathode, a pair of spaced control wires parallel to and insulated from each other and said cathode but spaced closer to said cathode than to said anode, one of said wires being positioned between said cathode and the central portion of one anode segment while the other wire is positioned between said cathode and the central portion of the other anode segment, a parallel tuned circuit connected to said control wires to supply opposite instantaneous potentials thereto, said anode segments and control wires being located in adjacent quadrants of a circle, a source of radio frequency input power coupled to said tuned circuit, and means for producing a magnetic eld acting transversely to the cathode-to-anode path.

5. A magnetron comprising an evacuated envelope, a cathode within said envelope and along the axis thereof, an anode including a pair of arcuate shaped anode segments around said cathode, a pair of spaced control wires parallel to and insulated from each other and said cathode but spaced closer to said cathode than to said anode, one of said wires being positioned between said cathode and the central portion of one anode segment while the other wire is positioned between said cathode and the central portion of the other anode segment, a parallel tuned circuit connected to said control wires to supply opposite instantaneous potentials thereto, said anode segments and control wires being arranged symmetrically on opposite sides of said cathode. a source of radio frequency input power coupled to said tuned circuit, and means for producing a magnetic field acting transversely to the cathode-to-anode path.

6. A magnetron amplifier comprising a cathode, an anode structure surrounding said cathode and having a plurality of spaced targets, a pair of spaced control wires parallel to and insulated from each other and said cathode but spaced closer to said cathode than to said anode, said wires being located on opposite sides of said cathode, each of said control wires being arranged between said cathode and one of said targets, means for producing a magnetic field acting transversely to the cathode-to-anode path, and means coupled to said control wires for supplying radio frequency power to said control wires in cophasal relation.

7. A magnetron comprising a cathode, an anode structure having a plurality of spaced target portions surrounding said cathode, a pair of spaced control wires parallel to and insulated from each other and said cathode, but spaced closer to said cathode than to said anode structure, means for producing a magnetic eld acting transversely to the anode-to-cathode path, each of said control wires being between said cathode and oneof said target portions, and leads connected to said control wires for supplying alternating current input power thereto.

8. `A magnetron comprising a cathode, an anode structure having a plurality of spaced target portions surrounding said cathode, a pair of spaced control wires parallel to and insulated from each other and said cathode, each of said control wires being between said cathode and one of said target portions, means for producing a magnetic field acting transversely to the anode-to-cathode path, a tuned circuit connected to said control wires to supply opposite instantaneous potentials thereto, and a source of input alternating current power coupled to said tuned circuit.

9. A magnetron comprising a cathode, a hollow cylindrical anode structure coaxially surrounding said cathode and including at least one pair of spaced anode segments of substantial circumferential length, a pair ofy control wires parallel to and insulated from each other and said cathode but spaced closer to said cathode than to said anode structure, each of said control wires being between said cathode and the mid-point of one of said anode segments, means for producing a magnetic field acting transversely to the anode-to-cathode path, and leads connected to said control wires for supplying control potentials thereto.

CLARENCE W. HANSELL.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Name Date Linder May 10, 1938 Dallenbach Aug. `30, 1938 Fritz et al. Mar. 28, 1939 Fritz June 20, 1939 Fritz July 18, 1939 IgIanselJ. Oct. 15, 1940 Number 

